This invention relates to melting furnace systems and methods of melting and more particularly to such systems and methods in which heat is applied within the mass of the melt constituents and in the region above that mass in a coordinated manner.
Heretofore it has been known to melt materials by developing heat within their mass and by applying heat external of their mass. In the discussion of this invention which follows these techniques and apparatus will be illustrated as applied to the melting and refining of glass. While certain aspects of the invention are particularly adapted to glass, particularly to Joule effect heating of molten glass having a negative temperature coefficient of resistance, it is to be understood that other heat softenable materials can be processed utilizing other features of the invention.
Glass has been melted in receptacles which include a closed top where heat is applied above the surface of the constituent mass as by the burning of fossil fuels within the enclosure or by electrical heating of resistors which adjust heat. It has also been heated or maintained molten by Joule effect heating involving the passing of electrical current between electrodes immersed in the constituent mass. Combinations of radiant heating and Joule effect heating have also been employed as where the preponderance of heat was derived from radiant heat, termed "electric boost" operation and conversely where the preponderance of heat was derived from Joule effect heating, particularly where fossil fuel was burned, termed "fossil fuel boost" operation.
Attempts have been made to coordinate heat input to melting furnaces with the heat required to establish and maintain desired conditions as by measuring the rate of feed of batch material into a melter and regulating the amount of heat supplied to the melter according to the batch feed rate as disclosed in Griem Pat. No. 3,573,017 of Mar. 30, 1971, for "Method and Apparatus for Melting and Supplying Heat-Softenable Materials in a Process." Another controlled melting approach is to alter the application of heat based on the level of molten material in the melter as disclosed in Trethewey Pat. No. 3,482,956 of Dec. 8, 1969, for "Method and Apparatus for Operating a Glass Melting Furnace."
While automatic or feedback control of melting operations have been utilized with some success they have generally been confined to a single form or region of heat application to the melt.